The present disclosure relates to a positive electrode active material, a method for manufacturing a positive electrode active material and a nonaqueous electrolyte battery.
In recent years, there has been an increased demand for small-sized and high-capacity secondary batteries along with the spread of portable appliances such as video cameras and laptop personal computers. Secondary batteries currently used include a nickel-cadmium battery and a nickel-hydrogen battery each using an alkaline electrolytic solution. However, the voltage of such a battery is low as about 1.2 V, and therefore, it is difficult to enhance an energy density. For that reason, studies have been made as to a lithium metal secondary battery using a lithium metal having a specific gravity of 0.534, a value of which is the lowest in solid elements, is also very poor in a potential and has the largest current capacity per unit weight in metal negative electrode materials.
However, in secondary batteries using a lithium metal for a negative electrode, when charged, dendritic lithium (dendrite) is deposited on the surface of the negative electrode and grows due to a charge and discharge cycle. Not only the growth of the dendrite deteriorates a charge and discharge cycle characteristic of the secondary battery, but in the worst case, the grown dendrite breaks through a diaphragm (separator) to be disposed so as to prevent a positive electrode from being in contact with a negative electrode. As a result, there gives rise to a problem that an internal short circuit is generated to cause thermorunaway, whereby the battery is broken.
In light of this, for example, as disclosed in JP-A-62-90863, a secondary battery in which a carbonaceous material such as cokes is used as a negative electrode, and charge and discharge are repeated by doping and dedoping an alkali metal ion was proposed. According to this, it has been noted that the foregoing problem of deterioration of the negative electrode in repeating charge and discharge can be avoided.
On the other hand, as a result of search and development of active materials showing a high potential as a positive electrode active material, those showing a battery voltage of about 4 V have appeared, and attention is paid thereto. Inorganic compounds such as alkali metal-containing transition metal oxides or transition metal chalcogens are known as such an active material.
In particular, lithium transition metal complex oxides composed mainly of nickel or cobalt, such as LixNiO2 (0<x≦1.0) and LixCoO2 (0<x≦1.0), are the most promising from the standpoints of high potential, stability and long life. Above all, lithium transition metal complex oxides composed mainly of nickel are a positive electrode active material showing a relatively high potential. By using such a lithium transition metal complex oxide in a battery, it is expected that the charge current capacity is increased and that the energy density is increased.
However, in secondary batteries using, as a positive electrode active material, a lithium transition metal complex oxide composed mainly of nickel, the gas generation in the inside of the battery is easily caused. For that reason, there was involved a problem that an internal pressure of the battery is easy to rise. In particular, in batteries using a laminated film for an exterior, there was involved a problem that the battery is easily swollen due to the gas generation.
In consequence, it is desirable to provide a positive electrode active material capable of suppressing the gas generation, a method for manufacturing a positive electrode active material and a nonaqueous electrolyte battery.